Disinfection Procedures for Private Water Wells
Coliform bacteria are indicators of potential contamination of a well
water supply and may originate from human, other animal, or soil
sources. If coliform bacteria are present, drinking the water may not
necessarily result in illness, but that possibility exists. Common
causes of coliform bacteria contamination in private water wells
include improper well surface seal and well maintenance without
disinfection. Proper sealing of the well and disinfection should be
performed to ensure a safe water supply and to verify that there are
no other sources of contamination that need investigation.
1. First, check to see that the well is tightly sealed to prevent the
entrance of any surface contamination, either solid or liquid, to the
water supply. Vents should be screened, opening down, and above
flooding. If the well is not sealed, take measures to have it sealed
properly, but allow capped ports for chlorine to be added to the well
now and in the future.
2. If applicable, notify tenants in advance that you are chlorinating.
3. Determine the amount of household laundry bleach
(5.25% sodium hypochlorite) to be added to obtain 100 parts per million
available chlorine in the well. for 6-inch diameter well casing, use 4.5
cups of bleach for every 100 feet depth of water in the well; for 8-inch
casing, use 2 quarts of bleach / 100 feet; for 10-inch casing, use 3 quarts
of bleach / 100 feet; for 12-inch casing, use 4.5 quarts of bleach / 100
4. Mix the bleach in approximately 10 gallons of water and pour the mixture
into the top of the well.
5. Open the first faucet beyond the water storage tank and start the pump.
When chlorine smell is detected from the faucet, connect a hose to the faucet
and spray the chlorinated water back into the well for about 5 minutes, trying
to have chlorine touch all the casing and piping surfaces inside the well.
6. Open every faucet / outlet in the system (outside first) and let the water
run. Limit the amount of chlorine reaching a septic system. Close each outlet
when chlorine is smelled from it and seal top of well. Allow to stand 12 to 24
hours. Do not drink or bathe in this strongly chlorinated water.
7. Starting with the outside faucets, open each water outlet and flush until
the chlorine is gone. It is best to use a swimming-pool chlorine test kit
after the smell is gone. We recommend using a bucket to collect inside
chlorinated water to avoid running too much chlorine into the septic tank.
Flushing can take many hours or even days. Monitor the use of your well pump
during flushing to avoid damage.
8. At least 5 days after the water is free of chlorine, resample the water for
coliform bacteria testing. For best results, keep the sample cool and get it
to a laboratory within a couple of hours. When a well is badly contaminated,
the above procedure may have to be repeated several times. If the well casing
is deteriorated or the well is not properly sealed, disinfection will not
prevent further contamination. Testing of private water samples may be done at
the Sutter County Public Health Laboratory, 1445 Circle Drive, Yuba City,